1. Field of the Invention
The present invention relates to a transmission, and more particularly to a manual transmission for use in vehicles.
2. Description of the Prior Art
In general, a conventional manual transmission comprises a housing which has one longitudinal end wall and the other longitudinal end wall and has a bottom defining a reservoir for lubricating oil. First and second bearings are disposed in upper and lower sections of the one longitudinal end wall of the housing, respectively. A third bearing is disposed in the other longitudinal end wall of the housing in an axially aligned relation to the second bearing. An input shaft adapted to be connected to an output shaft of an engine through a clutch is rotatably supported by the first bearing and has one axial end projecting outwardly of the housing and the other axial end projecting inwardly of the housing. An input gear is mounted on the other end of the output shaft for rotation therewith. A counter shaft parallel to the input shaft is rotatably supported by the second and third bearings. A counter gear is mounted on the counter shaft for rotation therewith and is in mesh with the input gear. At least a bottom portion of the counter gear is immersed in the lubricating oil within the reservoir. A bearing retainer is mounted on the outer surface of the one longitudinal end wall of the housing to retain the first and second bearings in their positons. The bearing retainer has therein an opening through which the input shaft extends. A ring seal member is disposed between the opening in the bearing retainer and the input shaft to seal an annular clearance therebetween.
In the conventional transmission described above, the first bearing supporting the input shaft is lubricated only by the lubricating oil scooped up by the counter gear and adhered to the first bearing when the input shaft is rotated to cause the counter gear to be rotated. The quantity of the lubricating oil spattered or splashed on the inner surface of the first bearing is in proportion to the rotational speed of the counter gear and/or the temperature of the lubricating oil, and is insufficient to lubricate the first bearing when the rotational speed of the counter gear and/or the temperature of the lubricating oil are or is low. The insufficient lubrication causes the temperature of the first bearing to be increased to result in the shortness of service life of the first bearing.
In addition, the seal member disposed between the opening in the retainer and the input shaft is lubricated only by the lubricating oil passing through the first bearing. There is little lubricating oil supplied to the seal member through the first bearing when the rotational speed of the counter gear and/or temperature of the lubricating oil are or is low. The seal member made of a resilient material such as rubber is apt to be deteriorated or degraded because of the insufficient supply of lubricating oil, thereby to cause a leakage of the lubricating oil to occur through the seal member.
The second bearing supporting the counter shaft is at least partially dipped in the lubricating oil within the reservoir, during the halt of the operation of the transmission. When the transmission is operated to cause the counter gear to be rotated, the lubricating oil within the reservoir is scooped up by the large diameter counter gear and is reduced to such a level that the substantially entire second bearing is exposed. Accordingly, during the operation of the transmission, the second bearing is lubricated only by a small amount of lubricating oil adhered to the second bearing prior to the rotation of the counter gear. The insufficient lubrication results in the increase in temperature of the second bearing and results in the shortness of service life thereof.